1. Field of the Invention
The present invention relates to a secondary battery, and more particularly to an inner pack type of a secondary battery capable of assembling a bare cell and a protective circuit module (PCM) in manner of a mechanical connection without performing a molding so that the assembly of the bare cell and the protective circuit module (PCM) can easily be performed as well as, if necessary, the disassembly and reassembly of the bare cell and the protective circuit module (PCM) can be performed, and at the same time their works can easily be performed.
2. Description of the Related Art
Generally, a secondary battery is capable of being charged and discharged unlike a primary battery that is not capable of being charged. The secondary battery has widely been used in small advanced electronic equipments such as a cellular phone, a PDA, a notebook computer, etc. In particular, since a lithium secondary battery has operating voltage of 3.6V that is 3 times higher than a nickel-cadmium battery or a nickel-hydrogen battery largely used as a power supply for electronic equipment and has high energy density per unit weight, the use of the battery rapidly increases.
Such a lithium secondary battery mainly uses lithium-based oxide as a positive electrode active material and carbon material as a negative electrode active material. And, the lithium secondary battery is manufactured in various types. As representative types, there may be a cylindrical type, a prismatic type, and a pouch type.
The configuration of the lithium secondary battery will briefly be described based on the prismatic type. The prismatic type of secondary battery includes a jelly-roll type of electrode assembly, which is formed by stacking and winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, a can having one side open to receive the electrode assembly, and a cap assembly sealing the open side of the can. Herein, the structure, which includes the electrode assembly, the can, and the cap assembly, is usually referred to as a bare cell. Such a bare cell may be considered one independent secondary battery.
The structure in which protective circuit module (PCM) is assembled into the bare cell is usually referred to as a core pack. Also, the secondary battery used for small electronic equipments, such as a cellular phone, a PDA, a digital camera, etc. is usually used in a form of a battery pack. Such a battery pack is made by packing the core pack including protective circuit module (PCM) and the bare cell through a molding and then wrapping them with a label, or is made by inserting the core pack in an outer case, which is usually referred to as a hard case.
Recently, a compatible built-in batter pack (hereinafter referred to as an inner pack), which is designed in a relatively simple form, is widely used for various kinds of small electronic equipments.
A general form of the inner pack is formed by disposing a PCM on a relatively long side of the bare cell and connecting the bare cell and the PCM through electrical connection member, and then molding the bare cell and the PCM with molding resin.
A process of molding the bare cell and the PCM by means of an insert injection molding will briefly be explained below. The process includes disposing the core pack, in which the bare cell and the PCM are electrically connected, in a molding space of a mold formed of an upper metallic mold and a lower metallic mold, and then injecting molding resin through an inlet of the upper metallic mold. Then, the injected molding resin is solidified to form a molding part.
However, as the conventional inner pack described above is molded with the molding resin for connecting the bare cell with the PCM, it should be subject to a troublesome working process of mounting the core pack in the metallic mold, injecting the molding resin in the molding space of the metallic mold, and separating the inner pack in which the molding part is formed from the metallic mold by means of the solidification of the molding resin.
Herein, since the molding resin once injected in the molding space can not be recovered again, the high accuracy of the process of injecting the molding resin is required, thereby causing difficulty in processing. And, even though high accuracy of the injection of the molding resin could be maintained, non-uniform injection cannot be prevented due to the characteristics of the molding resin, which is amorphous. Therefore, due to the defect of the molding part, the defective rate of the inner pack increases. Further, since the molding part in a viscous state is integrally formed with the core pack when the molding part is defectively molded, it is very difficult to perform a reworking.
Since the molding resin is injected in the molding space of the metallic mold at relatively high pressure, the high pressure to the molding resin is transferred to the core pack so that the arrangement of the bare cell and the PCM is disturbed, causing defect and misalignment.
Also, the molding resin shrinks in a solidification process. Therefore, if the molding resin is not uniformly injected in the molding space, the shrinkage of the molding resin is greater at a specific portion than other portions. This non-uniform shrinkage causes problems that the surface of the molding part becomes irregular and the specific portion collapses. Thereby, this problem causes the appearance defect of the inner pack as well as frequent contact defect while the completed inner pack contacts the electronic equipment.